Velocity gauge

ABSTRACT

A gauge capable of sensing the velocity at which it is displaced utilizing a pendulous mass dampened within a high viscosity oil, and utilizing polarized electromagnetic deflection means for deflecting the mass for test and calibration purposes.

PATENTED MAY 2 3 I972 SHEET 2 [IF 2 INVENTOR WlLLlAM D. PIERSONATTORNEYS VELOCITY GAUGE BACKGROUND OF THE INVENTION The inventionpertains to the art of velocity or displacement testing devices whereina pendulum member is located within a housing, and sensing means areassociated with the pendulum to indicate deflection between the pendulumand housing which is proportional to the velocity or other force imposedupon the housing.

Velocity type gauges have been used to sense shock waves travelingthrough the earth, and the gauge of the invention is particularlysuitable, and is commercially employed, for this purpose. In particular,there has been a need for velocity gauges in the testing of thecharacteristics of subterranean explosions, such as underground nucleardetonations.

In practice, velocity gauges used to sense the characteristics ofsubterranean explosions are buried at various depths within the ground,and some of the gauges are buried as deep as 400 or 500 feet. The holein which the gauge is buried is usually backfilled with concrete andgrout, and thus the gauges are not accessible once installed. In that itis necessary for a high degree of sensitivity to be achieved in order toproduce acceptable testing and evaluating data it is most necessary thataccurate calibration of the gauges prior to their actual use beaccomplished. With a pendulum type gauge it is usually necessary todampen the movement of the pendulous mass in order to produce optimumsignal characteristics, and the viscosity of the dampening liquid willvary with the temperature thereof. Thus, although the velocity gaugesmay be very accurately calibrated for a given temperature, thetemperature of the gauge once installed, may vary from that of thecalibration environment. While it is possible to estimate theapproximate temperature at which the gauge will exist duringinstallation and operation, it is not practical to accurately determinethis temperature, and this temperature will vary according to the depthat which the gauge islocated. In the past, gauges were calibrated at atemperature which would be approximately that at which the gauge wouldoperate. However, the actual temperature of the gauge in operationusually varies from that at which it was calibrated and inaccuraciesresult in the test data obtained.

It is known in the accelerometer art to incorporate self-testing ordeflection devices in a gauge. However, the prior art devices are of arelatively complex nature which do not lend themselves to theaforedescribed type of usage, and the state of the prior art isrepresented by U.S. Pats. Nos. 3,277,725 and 3,295,355.

SUMMARY OF THE INVENTION It is an object of the invention to provide avelocity gauge which may be buried in the ground, or located at aninaccessible location, whereby the gauge may be tested and calibratedwhile in operating situ in order to obtain the most accurate outputcharacteristics.

It is the purpose of the invention to provide a simplified constructionfor a velocity gauge using a sensing pendulous mass whereinelectromagnetic forces are used to deflect the mass for test purposes,and the degree of deflection may be very accurately controlled. Themagnetic forces imposed upon the pendulum are directly applied theretoand are polarized to deflect the pendulum in a given direction, and themass distribution on the pendulum is such as to provide optimumdeflection and sensing characteristics. For instance, in the preferredembodiment the pendulum is formed of a lightweight material, such asaluminum, and includes magnetic sensitive inserts adjacent 'its lowerend wherein the higher density of the pendulum is located at thatportion swinging through the greatest degree of movement. Additionally,the mass of the pendulum adjacent the free lower end thereof can befurther increased by the use of inserts of high.

density material, such as lead.

It is a further object of the invention to provide a velocity gaugeemploying a pendulous mass wherein the oscillation of the mass is sensedby a change of impedance between an armature mounted on the pendulum,and a coil located adjacent the armature and fixed with respect to thependulum axis.

Another object of the invention is to provide a velocity gauge whichemploys a pendulous mass surrounded by a viscous dampening liquid, andexpansion means are used in conjunction with the liquid in order toproduce substantially uniform pressure conditions within the gauge atdifferent temperatures, and to minimize variations in pendulumoscillation characteristics due to temperature variation.

BRIEF DESCRIPTION OF THE DRAWING The aforementioned objects of theinvention will be appreciated from the following description andaccompanying drawings wherein:

FIG. 1 is an exploded, perspective view of a velocity gauge constructedin accord with the invention,

FIG. 2 is an elevational, diametrical, sectional view taken through thevelocity gauge,

FIG. 3 is a detail, sectional view of the pendulum associated structureillustrating the pendulum being deflected from its normal at restcondition to its maximum testing condition,

FIG. 4 is a plan sectional view taken along Section IV-IV of FIG. 2,

FIG. 5 is an elevational, sectional view of the magnetic core assemblytaken along Section V-V of FIG. 1, and

FIG. 6 illustrates a modification of construction which may be utilizedwith the gauge when the gauge is to be horizontally mounted and thependulum is horizontally disposed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The velocity gauge includes anouter housing or casing 10 which may be of a cylindrical configuration.The casing includes an annular rib 12 for mounting purposes, and in use,the entire casing will be embedded within suitable support structurewithin the hole or other location in which it is to be located duringuse.

The casing 10 is internally threaded at its upper portion, and sealed bya cap 14 having an opening plugged by screw 16 and electrical terminals18 pass through liquid-tight connections. The cap 14 is maintained inposition by the annular nut 20 cooperating with the threads defined onthe casing.

The lower portion of the casing is provided with internal threads forreceiving an annular sleeve cap 22 which houses a bellows 24 of anaccordian-type formed of a flexible material mounted within a plate 26bearing against the upper end of the sleeve. An opening 28 is defined inthe plate 26 whereby the interior of the bellows 24 is exposed to theinterior of the casing 10.

A pivot axis for a pendulous mass 36 is defined adjacent the casingupper region by a pair of pivot members 30 received in extensions 32extending from the cap 14. The pivots 30 are fixed in place by setscrews 34. The pendulum 36 includes a pair of armatures 38 mounted uponradially extending extensions defined on the pendulum. It will be notedthat the armatures 38 are located adjacent the pivot axis and areinclined at about 5 to the vertical, and the armatures will thus move ina circular path upon deflection and oscillation of the pendulum. Thearmatures 38 are formed of a ferrous material capable of producing aninductance variation when used with its associated coil.

The armature coils 40 are mounted upon brackets 42 affixed to theunderside of the cap 14 wherein the core of the coils are radiallydisposed adjacent a pendulum mounted armature 38. Electrical conductors,not shown, are attached to the coils 40 and extend to the cap terminals18.

The pendulum 36 is preferably formed of a lightweight material, such asaluminum, and is of a plate configuration including bearings 44 at theupper region for permitting support of the pendulum upon the pivots 30.The lower region of the pendulum must include a material having amagnetic characteristic for attraction by the testing or cocking coil,and

when the pendulum is made of aluminum, holes are drilled in the lowerregion of the pendulum for receiving inserts 46 of a magnetic material.Also, in that it is desired that the center of mass of the pendulum belocated adjacent the lower regions of the pendulum, holes may be drilledwithin the pendulum for receiving high density material inserts 48, suchas lead, to increase the weight of the pendulum adjacent the lower endthereof.

Deflection of the pendulum 36 for testing purposes is produced by anelectromagnetic testing or cocking" coil assembly generally indicated at50 and located within the casing 10. The coil 50 includes a rectangularrecess 52 receiving the lower portion of the pendulum and windings inthe coil assembly produce the electromagnetic force for deflecting thependulum for test purposes. The coil 50 is energized through conductors54 extending through the bellows 24 to terminals which are connected toconductors extending to the testing and control equipment.

The core assembly 50 includes a steel U-shaped field piece having a base56 and upstanding legs 58. The base 56 is wound with wire 60 whichconnects to the conductors 54. The legs 58 are disposed on the lateralsides of the pendulum 36 and include inner surfaces 62 which arenonparallel and converge toward a stop screw, FIG. 4, as will be laterdescribed. The wire 60 is embedded in a potting compound, such asurethane, and this compound extends upwardly to define the recess 52,and give the assembly 50 a cylindrical peripheral configuration.

The upstanding portions of the coil assembly 50 in line with thedirection of movement of the pendulum are provided with inserts 64 forreceiving screws 66 and a stop screw 68 adapted to engage the pendulumlower end when deflected for testing purposes. By removing the leftscrew 66 the screw 68 may be rotated whereby the location of the innerend thereof with respect to the pendulum can be varied and thus it ispossible to very closely adjust the amount of swing produced by thependulum under test conditions.

In order to dampen the pendulum movement, and yet provide accuratemovement of the pendulum which may be accurately measured, the portionof the casing in which the pendulum is mounted is filled with a highviscosity oil such as a silicone oil having a viscosity variation ofapproximately 1 percent per F. Of course, any dampening liquid willexpand or contract as its temperature varies, and as the liquid in thecasing will communicate with the bellows 24 through the core assemblypassage 70 expansion and contraction of the dampening liquid will becompensated for by the bellows.

In operation, the velocity gauge will be buried in a hole adjacent theexplosion site, or at a position rather remote therefrom, depending uponthe test specifications. In the usual mode of installation the velocitygauge will be mounted in a vertical manner such that the pendulum 36will assume a normal orientation as that shown in FIG. 2, and the planeof the pendulum, and its axis, will be disposed substantiallyperpendicular to the direction from which the shock waves will bereceived.

Once the velocity gauge has been located in position, and connected byconductors to the testing equipment, the velocity gauge will assume thetemperature of its surrounding environment. After sufficient time afterinstallation has passed to permit the velocity gauge to assume thetemperature of its environment, calibration in situ may be accomplished.Such calibration is achieved by energizing the coil assembly 50, whichwill deflect the pendulum 36 toward the stop screws 68. Deflection ofthe pendulum toward the stop screw 68 is assured due to the polarizationachieved by the use of the nonparallel surfaces 62. In that the air gapbetween the magnetic inserts 46 decreases toward the stop screw 68, themagnetic force in the recess 52 will always move the pendulum in theproper direction toward the stop screw.

This deflection will permit the pendulum to be drawn into engagementwith the end of the stop screw 68. Thereupon, the

coil assembly 50 is deenergized, permitting the pendulum to swing backinto its normal, at rest, position. As the pendulum is swinging backtowards its normal position the movement of the armatures 38 withrespect to the coils 40 is sensed and recorded by the recordingequipment connected to the coils, and the time required for the pendulumto move through its desired arc, at the viscosity conditions under whichthe gauge will be subjected during operation, permits the gauge to bevery accurately calibrated.

In that the pendulum directly engages the stop screw 68, and as thearmatures 38 are directly mounted upon the pendulum, the apparatus is ofa relatively simple construction yet permits very accurate calibrationand operation signals to be produced.

In some instances it is desired to mount the velocity gauge in ahorizontal manner such that the pendulum 36 would be disposed in ahorizontal plane. With this type of installation the embodiment of FIGS.1 through 3 would not be able to accurately record velocities imposedupon the gauge in view of the influence of gravity on the pendulum. Toovercome the effect of gravitational forces in a horizontalinstallation, a counterbalance spring 72 is employed. The spring 72 isaffixed to an anchor 74 attached to the cap 14, FIG. 4. A spring anchor76 is affixed to the pendulum free end. The ofiset" relationship of thespring anchors 74 and 76 permits the spring to extend around thearmature 38 on the same pendulum side and the spring holds the pendulumin a substantially horizontal position, yet the pendulum will bepermitted to move up and down under influence of the testing produced bythe energization of the coil assembly 50, or under the influence ofdeflection produced by forces being opposed upon the gauge casing.

It is appreciated that various modifications to the inventive conceptmay be apparent to those skilled in the art without departing from thespirit and scope thereof, and it is intended that the invention bedefined only by the scope of the following claims.

We claim:

1. A velocity sensing device comprising, in combination, a casing,pendulum pivot means mounted within said casing defining a pivot axis, apendulum within said casing supported upon said pivot means having anull position, said pendulum including an oscillatable pendulous massportion, electrical sensing means within said casing sensing oscillationof said pendulum comprising a pair of armatures mounted on said pendulumadjacent said pivot axis and on opposite sides of said pendulum and anelectric inductance coil mounted within said casing adjacent each ofsaid armatures, an electromagnetic coil within said casing disposedadjacent said pendulum mass portion, magnetic means upon said massportion whereby energizing of said coil displaces said mass portion fromsaid null position, and a pendulum stop mounted Within said casingremotely spaced from the pendulum null position, said pendulum stopadapted to engage said pendulum mass portion upon said portion beingdisplaced toward said stop upon energization of said coil to providepredetermined pendulum movement upon deenergizing said coil forpermitting calibration of said device.

2. A velocity sensing device comprising, in combination, a casing,pendulum pivot means mounted within said casing defining a pivot axis, apendulum within said casing supported upon said pivot means having anull position, said pendulum including an oscillatable pendulous massportion, electrical sensing means within said casing sensing oscillationof said pendulum, an electromagnetic coil within said casing disposedadjacent said pendulum mass portion, magnetic means upon said massportion whereby energizing of said coil displaces said mass portion fromsaid null position, and a single pendulum stop mounted within saidcasing remotely spaced from the pendulum null position, said pendulumstop adapted to engage said pendulum mass portion upon said portionbeing displaced toward said stop upon energization of said coil toprovide predetermined pendulum movement upon deenergizing said coil forpermitting calibration of said device, said electromagnetic coil beingpolarized to deflect said pendulum mass portion toward said stop, saidelectromagnetic coil polarization including surface portions disposedadjacent the lateral sides of said pendulum mass portion, said surfaceportions being nonparallel and converging in the direction toward saidpendulum stop.

1. A velocity sensing device comprising, in combination, a casing,pendulum pivot means mounted within said casing defining a pivot axis, apendulum within said casing supported upon said pivot means having anull position, said pendulum including an oscillatable pendulous massportion, electrical sensing means within said casing sensing oscillationof said pendulum comprising a pair of armatures mounted on said pendulumadjacent said pivot axis and on opposite sides of said pendulum and anelectric inductance coil mounted within said casing adjacent each ofsaid armatures, an electromagnetic coil within said casing disposedadjacent said pendulum mass portion, magnetic means upon said massportion whereby energizing of said coil displaces said mass portion fromsaid null position, and a pendulum stop mounted within said casingremotely spaced from the pendulum null position, said pendulum stopadapted to engage said pendulum mass portion upon said portion beingdisplaced toward said stop upon energization of said coil to providepredetermined penduLum movement upon deenergizing said coil forpermitting calibration of said device.
 2. A velocity sensing devicecomprising, in combination, a casing, pendulum pivot means mountedwithin said casing defining a pivot axis, a pendulum within said casingsupported upon said pivot means having a null position, said pendulumincluding an oscillatable pendulous mass portion, electrical sensingmeans within said casing sensing oscillation of said pendulum, anelectromagnetic coil within said casing disposed adjacent said pendulummass portion, magnetic means upon said mass portion whereby energizingof said coil displaces said mass portion from said null position, and asingle pendulum stop mounted within said casing remotely spaced from thependulum null position, said pendulum stop adapted to engage saidpendulum mass portion upon said portion being displaced toward said stopupon energization of said coil to provide predetermined pendulummovement upon deenergizing said coil for permitting calibration of saiddevice, said electromagnetic coil being polarized to deflect saidpendulum mass portion toward said stop, said electromagnetic coilpolarization including surface portions disposed adjacent the lateralsides of said pendulum mass portion, said surface portions beingnonparallel and converging in the direction toward said pendulum stop.